Summary. Progesterone and oestrone alone or in combination were administered to sows during early gestation. A dose of 25 mg progesterone and 12\m=.\5 \g=m\g oestrone injected together for 10,5 or 2 consecutive days during the implantation interval caused increased litter size at term.The effect of exogenous steroid hormones on embryonic survival in the pig is unclear. While pro¬ gesterone given alone during gestation has no, or even a detrimental effect on embryo viability (Sammelwitz, Dziuk & Nalbandov, 1956;Haines, Warnick, Wallace & Edwards, 1957;Spies, Zimmerman, Self & Casida, 1959), the administration of progesterone and oestrogen has been re¬ ported to increase embryo survival (Reddy, Mayer & Lasley, 1958;Day, Romack & Lasley, 1963 Progesterone (A*-pregnen-3,20-dione: Sigma Chemical Co.) and oestrone (A1,3,5(10)-estratrien-3-ol-17-one: Sigma Chemical Co.) solutions were prepared as described by Reddy et al. (1958) and injected i.m. in volumes of 2 or 4 ml at invervals of 23-25 hr. The control and hormone treatments used are shown in Table 1. Control animals received cottonseed oil at corresponding times of treat¬ ment administration, but because there were no differences in mean litter size in the various subgroups, these results were pooled into one control group (Group 0).The number ofsows returning to oestrus, the number carrying the litter to term and the total number of pigs farrowed were recorded. Mean litter size was calculated and statistically tested by least squares regression analysis (Harvey, 1960).Conception rate was high in all treated sows and did not differ from that in controls. There was no effect of breed of sow or individual boar on litter size results (least squares regression analysis). As shown in Table 1, there was a significant increase in litter size when progesterone and oestrone were administered from Days 14-23 (Group 2), a period during which implantation is occurring (Green & Winters, 1946). Administration of both steroids for shorter intervals at this time resulted in increased litter size only in Groups 4 and 6. There was no effect of treatment on the number of pigs stillborn.

No abstract

Treatment of sows with 25 mg progesterone and 12.5 microgram oestrone daily between 14 and 23 days of gestation resulted in an increase of 15% of chorionic surface area and an increase in volume of allantoic fluid when examined at 30-35 days of gestation. In contrast, there were no significant differences in chorionic surface area or allantoic fluid volume between treated and control sows examined at 46-50 days of gestation. This suggests that progesterone-oestrone treatment of the sows during early pregnancy has only a short-lived effect on development of the allantochorion.

No abstract